This thesis consists of a fatigue study performed on a 2024-T3 aluminum alloy in the time domain and in the frequency domain. Random, non-zero mean stress and strain signals are analyzed in the time domain using the Rainflow method and the damage is accumulated by the Palmgren-Miner rule, according to the stress mean equations. Signals are analyzed in the frequency domain using the power spectral density, PSD, and the probability density function, PDF. The spectral domain analysis does not consider the negative effect of mean stress on metal fatigue life; therefore, the mean voltage correction factors developed by Goodman, Morrow and Smith-Watson-Topper are used to change the power spectral density and hence the damage is calculated by the probability density functions postulated by Dirlik and Tovo and Benasciutti. It was found that Dirlik and Tovo and Benasciutti are not conservative for a non-zero mean voltage signal when comparing the accumulated damage to that obtained in the time domain analysis. When the spectral method is corrected, however, the results vary from 4.9% for wideband signals to 6.8% for narrowband signals, always in the conservative zone, predicting further damage. The method of Tovo and Benasciutti 2 is considered as the spectral function with the closest results when compared to the Rainflow method, in the time domain.
